The United States Navy has also sent underwater search vehicles, and two undersea rescue systems, in order to help with the rescue effort.

On Wednesday, U.S. President Donald Trump tweeted, "I have long given the order to help Argentina with the Search and Rescue mission of their missing submarine. 45 people aboard and not much time left. May God be with them and the people of Argentina!"

I have long given the order to help Argentina with the Search and Rescue mission of their missing submarine. 45 people aboard and not much time left. May God be with them and the people of Argentina!

According to CNN, the San Juan has enough air to last only seven to ten days to remain fully immersed, but would have more time if the sub was raised to surface or "snorkeled," or refreshed using a tube raised to the surface.

Outside Mar del Plata navy base, the submarine's home base, Argentines like Federico Ibáñez waited for news about his brother Cristian, a radar technician on the San Juan.

Ibáñez slammed the country's navy for trying to ease concerns about the submarine.

"I think the navy is wrong in saying the submarine could be on the surface," Ibáñez said. "It's a lack of respect. If it was on the surface, they would have found it. They didn't, and they didn't look for them at the bottom."